In a known method for checking the. leak tightness of containers (U.S. Pat. No.5,161,408), the test object is subjected to a pressurized test gas, and the test gas escaping from test test object in the instance of a leak is subjected in an analyzing volume to an intensity-modulated electromagnetic wave field which is emitted by a laser, the wave field containing frequency components which are absorbed by the test gas, producing a photo-acoustic signal which is indicative of a leak. When the laser light is radiated into the analyzing volume with a frequency which is tuned to the absorption frequency of the test gas, a portion of the molecules of the test gas are excited to a higher state of energy by the absorption of the electromagnetic waves. Through collisions with other molecules in the analyzing volume the excited molecules may impart some or all of their excitation energy and transform the energy into translational, rotational or vibrational energy of the collision partners. The rise in translational energy of the molecules in the analyzing volume corresponds to a temperature rise and therefore a rise in pressure. When the intensity of the irradiation wave field is periodically varied, periodic pressure changes result, which can be detected by means of a pressure or acoustic sensor. As a test gas sulfur hexafluoride (SF.sub.6) can for instance be used, and the laser can be a CO.sub.2 -laser. In the known method the photoacoustic effect is used to localize a leak at the surface of the test object. It is not possible, though, to quantatively determine the size of the leak.
Based on this, it is the object of the invention to develop a method and a device for cheking the leak tightness of the type described above, with which a quantitative leak check may be performed with little expenditure.
For the solution of this object the combinations of features stated in patent claims 1 and 13 are proposed. Further developments and embodiments of the invention result from the dependent claims.